Electrodynamic microphone having a cardioidal directional characteristic



Oct. 27, 1970 scH N L 3,536,863

ELECTRODYNAMIC MICROPHONE HAVING A GARDIOIDAL DIRECTIONAL CHARACTERISTIC Filed Oct. 16, 1967 INVENTOR. GERRIT SCHENKEL 71M KL AGENT United States Patent Office 3,536,863 Patented Oct. 27, 1970 3,536,863 ELECTRODYNAMIC MICROPHONE HAVING A CARDIOIDAL DIRECTIONAL CI-IARACTERISTIC Gerrit Schenkel, Emmasingel, Eindhoven, Netherlands,

assignor, by mesne assignments, to U.S. Philips Corporation, New York, N.Y., a corporation of Delaware Filed Oct. 13, 1967, Ser. No. 675,129 Claims priority, applicatgtliglgetherlands, Oct. 22, 1966,

7 Int. Cl. H041 9/08, N20

US. Cl. 179121 Claims ABSTRACT OF THE DISCLOSURE The present invention relates to an electrodynamic microphone having a cardioidal directional characteristic and comprising a microphone capsule with a diaphragm, the space behind the diaphragm communicating with a central duct and with an air chamber surrounding said duct, while both the duct and the air chamber communicate through one or more openings with the rear side of the microphone capsule.

Such a microphone is known which has comparatively small dimensions. The said air chamber in this microphone is consequently also small, so that the frequency characteristic for the low tones is not satisfactory.

The invention is characterized in that a detachable adaptor is arranged on the rear side of the microphone capsule. This adaptor is provided with one or more chambers communicating with the duct and the air chamber in the microphone capsule.

The use of this detachable adaptor provides the advantage that the quality of the microphone capsule is materially improved, that is to say that a more satisfactory frequency characteristic is obtained in the range of the low tones. Moreover, the cardioidal directional effect in the low-tone range is materially improved. When starting from different adaptors, and with the same microphone capsule, a microphone can be composed which has different frequency characteristics or at any rate different directional characteristics. An embodiment according to the invention has an adaptor which is provided with a central duct axially merging into the ambient atmosphere and communicating with the central duct in the microphone capsule and further including an air chamber communicating with the openings in the rear wall of the microphone capsule.

An improvement in the acoustic properties can then be obtained by causing the central duct to communicate through one or more lateral duets with the ambient atmosphere.

A modification of this embodiment has lateral ducts in the form of grooves which may extend as far as the rear side of the adaptor.

All these embodiments according to the invention may be provided with an adaptor having an annular air chamber which communicates with one or more axial ducts which correspond to the openings in the rear wall of the microphone capsule.

Also for acoustic reasons, the ducts and/or the openings may be closed by acoustic resistances.

The connection between the microphone capsule and the adaptor is to be established so that the side of the adaptor cooperating with the rear side of the microphone capsule is provided with connecting lugs.

A particularly suitable adaptor comprises two interconnected parts arranged one behind the other, the first part including solely all the ducts and the second part only the central duct and a concentrically arranged cavity acting as an air chamber.

The invention will now be described more fully with reference to the accompanying drawings in which:

FIG. 1 is a longitudinal sectional view of an embodiment according to the invention,

FIG. 2 shows separately in perspective view a microphone capsule and an adaptor, and

FIG. 3 shows, likewise in perspective view, an alternative embodiment of an adaptor according to the invention.

In FIG. 1, a microphone capsule 1 of small dimensions has secured to it an adaptor 2 of the same diameter.

The parts together constituting the magnet system of the microphone capsule 1 consist of an annular permanent magnet 3, a soft-iron upper plate 4, a soft-iron lower plate 5 and a soft-iron shortcircuit ring 6. These parts are held together by a frame 7 of synthetic resin. The capsule 1 is further provided with a diaphragm 8 and a moving coil 9 connected thereto. This diaphragm is protected by an aluminium hood 10. The space 11 behind the diaphragm 8 communicates with a central duct 12 passing through the magnet 3 and extending as far as the rear side 13 of the microphone capsule 1.

The space 11 further communicates through an air gap 14 accommodating the moving coil 9 and through a duct 15 with an annular air chamber 16'. This air chamber 16 also communicates through an opening 17 with an annular cavity 18 in the rear side 13 of the capsule.

The adaptor 2 essentially comprises two parts composed of a synthetic resin: the front part 30 and the rear part 31. The front part 30 has a central duct 32 which is closed on the rear side by an acoustic resistance 33, for example, wadding, and which is in communication with the ambient atmosphere. Duct 32 communicates with four radial ducts 34.

The ducts 34 extend into the ambient atmosphere and are closed by acoustic resistances 35. Between the front part 30 and the rear part 31 is enclosed an annular space 40 which communicates with the front side 43 of the adaptor 2 through four axial ducts 41 closed by acoustic resistance 42. i

The location of the central duct 32 on the front side 43 of the adaptor 2 corresponds to the location of the central duct 12 on the rear side 13 of the microphone capsule 1. The location of ducts 41 on the front side 43 of the adaptor 2 also corresponds to the annular cavity 18 on the rear side 13 of the microphone capsule 1.

The adaptor 2 is secured to the microphone capsule 1 by means of lugs 50 which are provided on the front part 30 made of synthetic resin. These lugs 50 are clamped around annular parts 51 on the rear side 13 of the microphone capsule 1 which are also made of synthetic resin.

FIG. 3 shows an alternative embodiment of an adapter. The rear side 60 is directed to the right in this figure. The radial lateral ducts in this case have the form of grooves 61 extending as far as the rear side 60.

The adaptor also has a central duct 62.

What is claimed is:

1. An electrodynamic microphone having a cardioidal directional characteristic comprising, a microphone capsule having a diaphragm mounted therein, means defining an air space at the rear face of the diaphragm, means defining a central duct with an air chamber surrounding the duct and arranged so that the space behind the diaphragm is coupled with the central duct and with the air chamber surrounding said duct, means defining one or more openings in said capsule that couple the duct and the air chamber with the rear wall of the microphone capsule and a detachable acoustic adaptor member secured to the rear wall of the microphone capsule and provided with one or more chamber complementary with said openings in the capsule so as to communicate with the duct and the air chamber in the microphone capsule.

2. An electrodynamic microphone as claimed in claim 1 wherein said adaptor includes a central duct axially merging into the ambient atmosphere and coupled with the central duct in the microphone capsule, and an air chamber coupled with the openings in the rear wall of the microphone capsule.

3. An electrodynamic microphone as claimed in claim 2, wherein said adaptor further comprises means defining one or more lateral ducts that couple the central duct with the ambient atmosphere.

4. An electrodynamic microphone as claimed in claim 3, characterized in that the lateral ducts have the form of grooves.

5. An electrodynamic microphone as claimed in claim 4, characterized in that the grooves are axially oriented and extend as far as the rear side of the adaptor.

6. An electrodynamic microphone as claimed in claim 2 wherein the air chamber in the adaptor has an annular shape, said adaptor including one or more axial ducts which correspond to the openings in the rear wall of the microphone capsule and arranged to couple said openings with the adaptor air chamber.

7. An electrodynamic microphone as claimed in claim 3 wherein one or more of the ducts and openings are closed entirely or in part by acoustic resistances.

8. An electrodynamic microphone as claimed in claim 2 wherein the side of the adaptor co-operating with the rear side of the microphone capsule is provided with connecting lugs.

9. A microphone as claimed in claim 6 wherein said adaptor comprises two interconnected parts arranged one behind the other, the first part solely including all the ducts and the second part a central duct and a concentrically arranged cavity acting as said air chamber.

10. A microphone as claimed in claim 1 wherein said adaptor comprises, a central duct extending axially to mate with the central duct in said capsule, means defining an annular air chamber, means defining a plurality of axial ducts arranged to couple said adaptor air chamber with the openings in the "rear Wall of the capsule, and means defining a plurality of radial ducts that couple the adaptor central duct with the ambient atmosphere.

References Cited UNITED STATES PATENTS 2,401,328 6/1946 Black 179121 2,515,031 7/1950 Black 179-121 2,865,464 12/1958 Gorike 17912l 3,201,530 8/1965 Levy et a1 179-421 KATHLEEN CLAFFY, Primary Examiner T. L. KUNDERT, Assistant Examiner US. Cl. X.R. 179-115.5 

